This invention relates to thrust bearings and more particularly to tilting shoe type thrust bearings having a low resonant frequency when subjected to periodical axial loading.
Frequently, propeller shafts of new ships are subjected to serious longitudinal or axial vibration as inadvertently the critical speed of the shaft is such that the longitudinal vibration occurs near the full power operating speed of the shaft.
Hydraulic resonant chambers have been utilized to lower the overall stiffness of the thrust bearings by a factor of 4 or 5, thus dropping the longitudinal critical speed about 50 percent and lowering the critical speed to a value not frequently used and to one at which the load, stresses and propeller excitation values are greatly reduced. While hydraulic resonance changers are effective to reduce the longitudinal stiffness of the thrust bearing, they have experienced operational problems due to galling of the pistons and cylinders resulting in the cylinders and piston rods sticking or freezing. Hydraulic resonance changers are also expensive and require complex hydraulic circuitry to automatically equilibrate the propeller thrust.